Record neutron numbers at Sandia Labs’ Z machine fusion experiments

nuclear fusion
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A relatively new method to control nuclear fusion that combines a massive jolt of electricity with strong magnetic fields and a powerful laser beam has achieved its own record output of neutrons—a key standard by which fusion efforts are judged—at Sandia National Laboratories’ Z pulsed power facility, the most powerful producer of X-rays on Earth.

The achievement, from a project called MagLIF, for magnetized liner inertial fusion, was reported in a paper published Oct. 9 in the journal Physical Review Letters.

“The output in neutrons in the past two years increased by more than an order of magnitude,” said Sandia physicist and lead investigator Matt Gomez. “We’re not only pleased that the improvements we implemented led to this increase in output, but that the increase was accurately predicted by theory.”

MagLIF neutron production increased to 10 to the 13th using deuterium fuel (10 to the 15th would represent the hundred-fold output increase generally accepted by scientists, if an equal mixture of deuterium and tritium, DT, had been used) and the average ion temperature doubled. This was achieved through a simultaneous 50 percent increase in the applied magnetic field, a tripling of laser energy and an increase in Z’s power input from 16 to 20 mega-amps, Gomez said.

“The output was only 2 kilojoules DT, a relatively small amount of energy,” he said. A kilojoule is defined as the heat energy dissipated by a current of 1,000 amperes passing through a 1-ohm resistor for one second. “But based on the experiments that we have done so far, which show a factor of 30 improvement in five years and simulations consistent with those experiments, we think that a 30 to 50 kilojoule yield is possible, bringing us near the state known as scientific break-even.”

The rise in output, predicted from changes in input, indicates that a proposal to build a machine even larger than Z and better equipped to exceed break-even, now has a stronger basis from which to make that request, said Gomez.

“Results at MagLIF have stirred a tremendous interest in fusion research that —by combining magnetism, lasers and electrical energy—spans the plasma states between traditional inertial confinement fusion, like the lasers at Lawrence Livermore National Lab’s National Ignition Facility, and traditional magnetic confinement fusion like the international ITER project in southern France,” said Dan Sinars, director of Sandia’s Pulsed Power Sciences Center. “MagLIF’s success has led to new programs and several fusion start-ups, and has helped build interest in this broader approach.”

Because performance and plasma conditions varied predictably with changes in input parameters, Sandia fusion experiments manager David Ampleford said, “We have additional confidence we can scale MagLIF to higher currents.”

Break-even is the intermediate goal

Break-even occurs when the amount of energy invested in the fuel is equal to the amount of energy it emits, a milepost achievement to those in the field. When more energy is emitted than is needed to maintain the experiment—a condition known as “high yield”—the world’s dream